Gradient index glass has been used to make the "Woods's Lens". In the prior art, the index of refraction of a flat piece of glass is increased toward the center, in such a way that the flat glass focuses the light. In this application, a reversed index is used to make a curved ogive have the optical properties.
Current laser designator weapon systems are required to use hemispherical shaped windows on the seeker to obtain the necessary optical quality for guidance. The aerodynamic performance of the missile is reduced because the hemispherical shape introduces a large drag coefficient.
The seeker window of the present invention is constructed with an index of refraction which varies as a function of position off the axis of the cylindrical missile.
The window as set forth herein reduces the drag coefficient on laser designator weapons and increases their effective range without a reduction in the optical performance.